How Clients and Servers Work Together

Objectives Learn about the interaction of clients and servers Explore the features and functions of Web servers

A server can be software that provides a service to other software or the computer on which the server software is running. Consider a server as a software application that must be installed and managed by someone with the title of system administrator, network administrator, or, for Web servers, Webmaster. Understanding How Clients and Servers Interact

User Interfaces: GUI Versus Command-Driven When you use a command-driven interface, you type commands into a user interface to perform a task and achieve a desired result. In contrast to a command-driven interface, a graphical user interface (GUI) has icons or menus that you can select to perform a function or run a program.

User Interfaces: GUI Versus Command-Driven (Continued) Applications that run on computers and servers can also be controlled by configuration or initialization files. An initialization file (INI file) is an ASCII text file with a.ini file extension.

Client/Server Sessions Transmission Control Protocol (TCP) manages the three-way handshake that establishes a session to be used by application protocols, such as HTTP or FTP.

Tracking Information in Log Files Servers and client applications often track information about their activities in log files. These are text files that administrators can use to troubleshoot problems with the software, to track activities to analyze traffic patterns or user preferences, or to look for clues indicating that hackers are using the server.

All-in-One Clients As the number of applications that use the Internet grows, the need for client software on computers to use these applications also grows. One solution to the growing number of Internet applications is an all-in-one client or universal client. These clients can handle several applications and adjust appropriately, changing buttons and functions to accommodate each application. Microsoft Internet Explorer is a good example of an all-in-one client.

Exploring the Features and Functions of Web Servers A wide variety of Web servers are available, many of which you can download for free. Some popular Web servers include the following: –Apache Web Server –Microsoft Internet Information Services (IIS) –Border Manager –Netscape Enterprise Server (NES)

Ability to Support Virtual Servers and Virtual Hosts A Web server should be able to support virtual servers and virtual hosting. Most virtual hosts handle multiple domain names on the same server by having the Uniform Resource Locator (URL) serve as a path to a file.

Protocols Supported All Web servers support HTTP, and some also support FTP so developers can send files to the site from remote locations. If you want to use your Web server for e- mail, the server must support protocols.

Access Control Based on the user’s IP address or user ID, access control allows the Web server to limit to which files a user can read or write. User Ids are associated with passwords to verify a user’s identity. Another method of access control is changing the port at which a server is listening. Port 80 is the default port for Web servers. Apache Web Server controls access to its resources via a process known as authentication, which requires a user to enter a valid user ID and password to access a Web site.

Access Control (Continued)

Encrypting Protocols A secure protocol used by Web servers is SSL (Secure Sockets Layer). When you see a URL with https: at the beginning instead of you know that this Web server is using the SSL protocol for security.

Chroot Mode Chroot mode restricts the portion of the file system that the server occupies. Running in chroot mode offers security because all private files can be kept outside of the server area.

Server Side Scripting A script is a short list of instructions that certain software can perform. The instructions must be written in a format called a scripting language. Popular scripting languages include Perl, VBScript, and JavaScript.

Standard CGI-Based Scripts Common Gateway Interface (CGI) is the set of specifications that defines how a Web server passes a Web user’s input to an application program running on the server, receives a response, and passes data back to the user. One advantage of CGI scripts is that they are consistent among operating systems.

Server-Side Include (SSI) Server-Side Include (SSI) is a simple form of scripting that allows you to include variable values in HTML code before it is sent to the browser. SSI scripts insert a line in the HTML file that indicates a variable value needs to be entered before the file is sent to the browser.

Database Interfaces Before selecting a Web server or a virtual hosting service, find out what databases the server supports and what tools can exchange information with the database. Popular databases are MS Access, MySQL, Oracle, and SQL Server.

Ability to Monitor Performance Microsoft IIS uses Performance Monitor, a program that comes with Windows Server 2003 and Windows 2000 Server, to monitor performance. Other utility programs are Microsoft Web Capacity Analysis Tool (WCAT) and Server Check Pro by NetMechanic.

Summary A server can be software that provides a service to other software or the computer on which the server software is running. TCP creates sessions that application protocols, such as HTTP and FTP, can use. Apache Web Server by the Apache Software Foundation is a common Web server that runs on a UNIX or Windows platform.